Even though certain well know companies in Europe and the USA have developed diesel aircraft engines, they have not found favor in actual applications, as they were affected by considerable handicaps and deficiencies. The fact is that at the present time not a single diesel aircraft engine is in use or production anywhere in the world-
In particular, the specific weight per unit power, of these experimental engines was within a range of 1.5 to 1.0 kp/PS, which represented a significant disadvantage relative to the most favorably regarded spark ignition gasoline engines with about 0.95 to 0.60 kp/PS. (The higher value relates to small engines, the lower value to engines from about 900 PS on.) The exceptions are certain engines for military aircraft beginning at about 1 400 PSm with roughly 0.45 kp/PS.
The specific fuel consumption of the experimental diesel aircraft engines of 195 to 165 g/(PS/h) was not sufficient to justify the high weight by unit power or to compensate for it, even over longer flights.
The reason of the much higher weight of diesel engines--in their configurations prevalent heretofore--compared to spark igniters, are adequately known, i.e. the compression and combustion pressures are approximately twice as high or even more, as that of as spark ignition engines.
The higher static and dynamic stresses to which conventional diesel engines are exposed necessarily lead, in view of the larger dimensions required, to higher weights, for example: heavier crankshafts, heavier connecting rods, requiring heavier counterweights, bearings, housings and also heavier cylinder heads.
In a manner similar to vehicle design, the demand for diesel engines for aircraft appeared only after the "energy crisis". Today, however, a need for such engines is clearly audible in the professional literature. A principal reason is the high and still rising energy prices. Further reasons, not less important, are the significantly longer flight durations and ranges, together with higher payloads with identical tank capacities, because the specific fuel consumption of a good diesel engine, with direct injection, which is less by 25 to 35% than the gasoline engines presently in use, is able to provide certain savings.
The clearly improved operating safety, due mainly to the absence of ignition devices, which are the source of many of all problems, and the elimination of the danger of fire due to the inflammability of diesel oil being above 55.degree. C., are hard advantages relative to gasoline engines.
The economic and safety advantages of diesels relative to the present gasoline engines are generally know. However, the problems involved in the design of such a diesel engine with all of these advantages, but without the disadvantages, are not known as well.
The most important differences up to now are:
(a) gasoline aircraft engines: PA0 (b) diesel aircraft engines: (experimental unit) up to now:
1. Weight by unit power: relatively good PA1 2. Specific consumption: relatively high PA1 3. Reliability: acceptable PA1 1. Weight by unit power: too high PA1 2. Specific consumption: optimal PA1 3. Reliability: very good
Consequently, if a way could be found to reduce the specific weight by unit power of the diesel engine, all of the advantages would be attained. As the requirement of an optimum specific weight cannot be realized, there exists a need for a novel technology.